2H-NbSe2, a layered transition metal dichalcogenide, offers an ideal platform for the study of superconductivity from a bulk system to two-dimensional limit. In our work, differential conductance spectroscopy was exploited to probe the superconductivity in a few-layer NbSe2-graphene heterojunction. Owing to the gate-tunable Fermi level of few-layer graphene, the sensitively gate-dependent differential conductance allowed us to investigate the superconducting gap structure of NbSe2 with continuously tuned junction transparency between tunneling regime and Andreev reflection limit. Features of two-gap superconductivity in NbSe2 were observed with a characteristic differential conductance of a central dip and two sets of coherence peaks when the Fermi level was finely tuned to the charge neutrality point of the junction. Through Blonder-Tinkham-Klapwijk fits, two gaps along with their temperature dependence were extracted. The gap to Tc ratio resulted from the fits and the temperature behavior of the two gaps were further analyzed and discussed, pointing to a weak to moderately strong coupling scenario for the few-layer NbSe2.

*Financial support from the Research Grants Council of Hong Kong (Project 16302215, HKU9/CRF/13G and 16300717) is hereby acknowledged.